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Aggregate Functions

Group By II

Sometimes, we want to GROUP BY a calculation done on a column.

For instance, we might want to know how many movies have IMDb ratings that round to 1, 2, 3, 4, 5. We could do this using the following syntax:

SELECT ROUND(imdb_rating), COUNT(name) FROM movies GROUP BY ROUND(imdb_rating) ORDER BY ROUND(imdb_rating);

However, this query may be time-consuming to write and more prone to error.

SQL lets us use column reference(s) in our GROUP BY that will make our lives easier.

  • 1 is the first column selected
  • 2 is the second column selected
  • 3 is the third column selected

and so on.

The following query is equivalent to the above:

SELECT ROUND(imdb_rating), COUNT(name) FROM movies GROUP BY 1 ORDER BY 1;

Here, the 1 refers to the first column in our SELECT statement, ROUND(imdb_rating).

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